Bilge oil is an omnibus term for oil that is normally collected at the bottom of the hull of the ship in the so called bilge tank. Bilge oil may originate from oil leakage in the transmission and/or in the main seals of the engine. In addition, volumes of water, typically containing different kinds of detergents, generated during the normal operation of the ship in, for instance, the engine room are likewise collected in the bilge tank. In ships that are not provided with a bilge tank, bilge water and oil that are to be transferred to the separator are preferably collected in a keel section of the ship and/or in a bilge well. Said liquids may also frequently be observed in the engine room of the ship. Bilge oil, having lower density than bilge water containing detergents, floats on the bilge water surface. A bilge water separator, standard feature on most ships having gross tonnage that exceeds 400 tons, is normally used to separate the oil from the water. A pump and a thereto connected suction hose, whose open end is positioned at the bottom of the bilge tank, are normally used to transfer the content of the tank into the separator. Accordingly, the bilge water needs to first be removed from the bilge tank, and only thereafter may the bilge oil be removed therefrom. As a consequence, harmful oil may very frequently be observed in the bilge tank since water is continuously flowing into the tank and the above-mentioned pump has limited capacity.
Admittedly, certain of the above-mentioned detergents are capable of binding to the oil molecules, whereupon this new compound sinks to the bottom of the bilge tank for a subsequent evacuation into the separator. A portion of the oil from the water surface is hereby removed, but the method is rather expensive and environment-unfriendly since it requires significant amounts of detergent. Furthermore, said separator is rather inefficient, when large amounts of detergents are mixed with the water and/or oil.
Accordingly, current solutions for bilge water management are ridden with significant drawbacks.
U.S. Pat. No. 6,905,611 discloses a device for separating a surface layer of a liquid by a container submerged in the liquid. The container includes a bottom, a wall member, connected to the bottom and having a variable length, and a separating member, which is connected to the wall member and communicates with a space in the container via an opening. An overflow portion of the separating member is located below a free liquid surface of the surface layer. A discharge conduit extends from the space for liquid discharge. The device further comprises a floating and a submerging member that contribute to proper positioning of the overflow portion of the device relative to the liquid surface.
However, the design, as disclosed in U.S. Pat. No. 6,905,611, comprising the floating and the submerging member, renders the device bulky, deteriorating as a result its performance in narrow spaces, such as tanks found onboard ships. Moreover, when the liquid to be removed passes said overflow portion on its way into the container, the entire device is effectively submerged. As a consequence, the separating process cannot be efficiently controlled, especially on a wavy liquid surface, where occasionally only a section of the overflow portion of the device is submerged. For the same reason, the device is not suitable for removing thin layers of liquid.
In addition, the overflow portion, that is necessary for proper functioning of the device and is a structurally integrated part of the floating member, exposes the latter, and thus the entire device, to the buoyant force of the liquid held in the tank. This calls for a counterbalancing force having opposite direction in order to properly position the device relative to the surface of the liquid. Said counterbalancing force is achieved by means of the submerging member. Forces thus exerted on the device increase its operative complexity.
Moreover, the highly probable entrapment of at least a portion of the skimmed liquid by other components of the device, such as on top of the separating member, deteriorates its performance and increases its maintenance frequency.